HL 1 Biology

3.1 Chemistry of Life

Element: a material made up of one kind of atom

  • are pure substances
  • consists of its own unique chemical and physical properties
  • most common elements found in living things: carbon, hydrogen, oxygen and nitrogen
  • Examples:
      • Sulfur = component of some amino acids
      • Phosphorus: component of nucleotides in DNA + RNA
      • Iron = a role in oxygen transport in animal blood & component of cytochrome proteins in electron transport in plants, animals and prokaryotes
      • Sodium = in nerve impulses in animals + in some halophilic bacteria; essential for maintaining metabolic activities. *NOT essential in most plants (though some can be used to maintain osmotic balance)

Molecule: when two or more atoms are chemically combined, through formation of a covalent bond

  • WATER: molecule formed by an oxygen atom and two hydrogen atoms
      • has unequal charge distribution: hydrogen and oxygen involves unequal sharing of electrons (a polar covalent bond)
      • water molecules stick together because of the formation of “hydrogen bonds” (unequal charge distribution cause hydrogen to have partial positive charge and oxygen to have a partial negative charge)
  • Hydrogen bond:type of intermolecular force formed when a hydrogen in one polar covalent molecule attracts to slightly negative atom of another polar covalent molecule
      • gives water its unique properties which are important to living things
      • *cohesion: binding together of two molecules of the same type (e.g. 2 water molecules)
      • Term “bond” misleading because:
          • its an interaction between molecules, not like a molecules covalent bond
          • it does not change in the chemical properties of its constituent particles (like how covalent bonds would)
          • Its absolutely weaker than a covalent bond/ionic bond
  • Properties of water
      • cohesive properties of water
      • thermal properties of water: has a high specific heat capacity (resists changes its temp.), boiling point of 100 degrees Celcius, water can evaporate at temps below boiling point
      • solvent properties: polar nature of water molecules, forms shells around charged + polar molecules to stop the from clumping together.
      • *water is used as a coolant, a medium for metabolic reactions and as a transport medium living organisms.

Ion: the electric charge of an atom or molecule


Elemental Composition of Living Organisms (p.44)

1) carbon, hydrogen and oxygen

2) (a) Canis: Nitrogen, calcium

(b) Chara: Potassium, calcium

3 (a) Canis has nitrogen of 82mg g-1 and Chara has nitrogen of 22mg g-1. Therefore, there is at least a 62mg g-1 difference between the nitrogen composition of the two. Also calculated as: (82-22)/22*100% = 273%, thus Canis has 272% greater nitrogen composition than Chara.

(b) Canis (dog) may have more proteins and amino acids compared to Chara resulting with a higher nitrogen content. Because the Canis consists of much protein, the organism contains skeletal-muscles as well which also effects its high level of nitrogen content.

4) Looking at the data, Canis has a higher level of nitrogen, calcium and phosphorus compared to Chara. Yet Chara has a greater level of potassium and magnesium than Canis. Both the Canis and Chara have the same level of sodium and sulfur. Chara lacks cl whereas Canis does not consist Mn in the organisms. Overall, Canis has a higher mass of elemental composition per mg g-1 dry matter than Chara.


One thought on “3.1 Chemistry of Life

  1. Grade 7 A consistent and thorough understanding of the required knowledge and skills, and the ability to apply them almost faultlessly in a wide variety of situations.

    1. Nitrogen, Calcium and potassium
    2. a) Nitrogen, Calcium     b) Potassium, Calcium
    3. a) Chara 22 mg g-1. and Canis 82 mg g-1; [(82 – 22)/22] x 100% = 272% higher nitrogen content in Canis  b) Canis is an animal and contains more protein than Chara, which is plant; Nitrogen helps build protein thus there is more Nitrogen for Canis.
    4. Canis has higher nitrogen, phosphorus and calcium; On the other hand, Chara has higher Magnesium and Potassium; The total mass of elements per g dry matter is higher in Canis;. Sodium and Sulphur’s level are the same in both graphs; Canis has an insignificant amount of Mn/Chara has an insignificant amount of Cl

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